Conventionally, at a fuel electrode in a methanol fuel cell, a methanol aqueous solution is consumed through a chemical reaction and carbon dioxide gas is produced. A gas-containing liquid comprising carbon dioxide gas and unreacted methanol aqueous solution is thus discharged from the fuel electrode side of the cell stack of the liquid fuel cell. The unreacted methanol is fed into a fuel adjusting chamber, and methanol and water are added in the fuel adjusting chamber to adjust to an optimum concentration and thus enable reuse; for this, it is necessary to separate out and discharge the bubbles of carbon dioxide gas from the gas-containing liquid.
A conventional gas-liquid separator used in a liquid fuel cell has a constitution in which the gas-containing liquid is separated into the gas and the liquid by gravity in a separating vessel, the gas is discharged from a gas outlet provided at the top, and the liquid is removed from an outlet provided at the bottom. The gas outlet at the top is closed off by a gas-liquid separating membrane that blocks the passage of the liquid and allows only the gas to pass therethrough, this being to prevent leakage of the liquid upon overturning. Such a constitution is proposed in, for example, Patent Document 1 (Japanese Patent Application Laid-open No. 4-229958, pages 2 to 3, FIG. 1) and Patent Document 2 (Japanese Patent Application Laid-open No. 11-128605, pages 2 to 3, FIG. 1).
Moreover, another example of a conventional gas-liquid separator is a gas-liquid separator used in a liquid degasifier. With this gas-liquid separator, hydrophobic porous hollow fiber membranes through which water passes with difficulty are disposed in a gas outlet, and hydrophilic porous hollow fiber membranes through which air passes with difficulty are disposed in a liquid outlet, and the two types of hollow fiber membranes are combined adjacent to one another. This constitution is proposed in, for example, Patent Document 3 (Japanese Patent Application Laid-open No. 7-265634, pages 2 to 3, FIG. 1) and Patent Document 4 (Japanese Patent Application Laid-open No. 9-313806, pages 2 to 4, FIG. 1).
However, with a gas-liquid separator having a constitution in which gravity is used as in Patent Document 1 or 2, if the gas-liquid separator becomes upside down, then a problem will arise in that the gas-liquid separating ability will be lost, this being due to the gas outlet which is now at the bottom being blocked by the liquid and hence the outlet for the gas being lost, the gas which is lighter than the liquid flowing out into the liquid outlet which is now at the top, and so on.
On the other hand, with a gas-liquid separator having a constitution in which porous hollow fibers and tubes are used as in Patent Document 3 or 4, the porous hollow fibers are expensive, and hence the apparatus itself becomes expensive. Moreover, the technique of disposing a large number of hollow fiber membranes and hermetically sealing the ends of the hollow fibers in the outlet region is difficult, and hence the apparatus cannot be made thin and small. Furthermore, a large amount of a filling adhesive is used in sealing the large number of porous hollow fibers, and hence leaching out of impurities from the filling adhesive into the solution becomes prone to occurring, and hence application to a solvent-based aqueous solution having high solubility toward resinous adhesives is not possible, and thus the range of solvents that can be used is narrow; there are thus many problems.